Planning For A Solar Sky ShowOn May 20th, skywatchers in the western third of the United States will be treated to an annular solar eclipse, a sight not seen here in 18 years. Dean Regas of the Cincinnati Observatory shares tips for viewing the eclipse, and tells how solar observers can safely get a peek at the elusive 'ring of fire.'

On May 20th, skywatchers in the western third of the United States will be treated to an annular solar eclipse, a sight not seen here in 18 years. Dean Regas of the Cincinnati Observatory shares tips for viewing the eclipse, and tells how solar observers can safely get a peek at the elusive 'ring of fire.'

IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. Paralyzed from the neck down, unable to speak after a stroke, Cathy Hutchinson hadn't been able to drink anything without the help of a caregiver for 15 years now, and later in the program we're going to talk about what happened with the robotic arm that was used to help her restore her function, and that'll be coming up this hour.

Also, we're going to talk about another, well, development in robotics research, having to do with the brain. But first we're going to talk about an eclipse and how that is scheduled to happen this weekend, and if you're in the western part of the U.S., a great treat awaits you this weekend, the chance to see an annular solar eclipse.

It's, you know, it's not the total eclipse, the classic one, the kind of - this one looks like a ring of fire with the moon fitting right inside the sun. It's a view that we haven't had in this country for the past 18 years. How can you see it safely? Joining me now is Dean Regas. He's the outreach astronomer at the Cincinnati Observatory and co-host of "Star Gazers" program on PBS. Welcome to the program.

DEAN REGAS: Oh, thanks for having me. I'm very excited about this eclipse. Only two days to go, Ira.

FLATOW: Two days.

(SOUNDBITE OF LAUGHTER)

FLATOW: You're an eclipse chaser, is that right?

REGAS: OK, where did - I kind of gave that away, didn't I? I'm very excited about this eclipse. In Cincinnati, we aren't going to be able to see it very well. So I am traveling to the beautiful city of Reno, Nevada, to be right in the right place at the right time.

FLATOW: Aha, and what makes this eclipse different than the total solar eclipse we're used to?

REGAS: Well, in this case the moon isn't big enough to block out the entire sun. Or to be more precise, the moon is farther away from the Earth. So every once in a while, the moon, you know, it has the cycle where it gets closer and farther. Listeners might remember a few weeks ago where we had the supermoon, where the moon was really close to us.

FLATOW: Right.

REGAS: Well, on Sunday the moon is going to be wimpy. It's going to be far away from us, and it won't be able to block out the entire sun. So it'll like a ring around the moon, the ring of fire, the eclipse.

FLATOW: Uh-huh. And why is it so hard to see? Why do you have to be in a right spot, and where is that spot?

REGAS: Well, it's a very narrow path. I mean, we have this great, interesting thing with the sun and the moon: They both appear to be the same size in the sky from Earth. It's this very rare thing. And so when they line up just right, it's a very narrow path where the shadow comes down.

So for this eclipse on Sunday, you have to be - it starts over in China and Japan, and then in the United States it crosses in Northern California, then through Nevada, Utah, Arizona and ends in West Texas.

FLATOW: As a planet, we're pretty unusual in having eclipses like this...

REGAS: Oh yeah, I mean it's amazing. We have just this interesting situation where the moon and the sun, I mean think about it. They're both about the same size in the sky, and to get these perfect total eclipses, I mean, that's just as rare as it gets. You get everything lined up just perfectly.

And for astronomers like me, we get all excited about this. I mean I've had this date on my calendar for a while. And so we plan way far ahead of time, and I just kind of get hooked on eclipse chasing, and it's a good excuse to go for a vacation too.

FLATOW: Yeah, so tell us exactly where you have to be if you want to see this eclipse.

REGAS: Well, anywhere west of the Rockies or west of the Great Plains, you're going to see a partial eclipse. So part of the sun will be blocked out. But the exact path, it's a very narrow path, you know, through Northern California. You go through Reno, and then it goes through Albuquerque, New Mexico. I definitely have to get a shout-out to Albuquerque too. And then ends in West Texas.

But anywhere - that's where you'll see the annularity, where the - that's the path of annularity where you can see the ring of the sun around the moon. But anywhere west of the Great Plains you'll see at least a partial eclipse.

FLATOW: This is really a narrow spot. You have to really go out and find it and chase it like you do.

REGAS: Exactly, exactly.

FLATOW: How often does this happen? This is quite rare, is it not?

REGAS: Yeah, we haven't had an annular eclipse in the United States since 1994, and this is part of what's called a sero-cycle(ph) that repeats itself every 18 years, 11 days and six hours - but who's counting that? But it repeats itself very precisely, and so we'll have another eclipse just like this 18 years, 11 days and six hours from now.

FLATOW: And in a couple of weeks, there's going to be another big sky show, right? The Transit of Venus. Tell us about that.

REGAS: Oh, this is - this is about the rarest of the rare thing you could see. This is when Venus crosses in front of the sun. We had this happen in June 2004, but we're going to have a repeat here June 5, 2012. And we need to urge everybody to go see this thing because we are not going to live to see the next one. The next time this'll happen will be the year 2117.

Now, it's not quite as dramatic as a solar eclipse or anything like that, it's a little subtle, and may I do my sting impression? Is that OK?

FLATOW: Go ahead.

(SOUNDBITE OF LAUGHTER)

REGAS: (Singing) There'll be a little black spot on the sun that day.

All right, I was paraphrasing "The King of Pain," but anyway, it's - you'll be able to see a little black spot go across the sun, and of course this is - looking into the sun is very, very dangerous. So safety is first, definitely.

FLATOW: And what kind of safety are we talking about here?

REGAS: Well, approved solar filters are what you really need. The cheapest and I think probably the best way is to go with these welder's glasses. They're called number 14 welder's glasses. They're a very dark shade. You go into a welding store, and you say you want number 14, they know what you're doing. They always look at me and they say, oh, you're going to look at the sun? I say yeah, that's what I'm going to do.

And so you want to get those glasses. They usually cost about five, six bucks or so. And then you can put those up to your face and look right at the sun all you want. Then you can also get filters for your telescopes, binoculars, that type of thing. But really, we recommend making this into a social situation.

As astronomers, we always like company, and we recommend people to join or find any astronomical groups that are in their area, because there are astronomy clubs all over the country, and they love to share their expertise, and on these days of the eclipse on the 20th and the Transit on the 5th, join up with one of them because it's a lot of fun having a sun party.

FLATOW: Wow, and you can find these - you can find more information on your website, or...

REGAS: Well, you can go to cincinnatiobservatory.org, is a good place to start, and there's also some great websites out there. Astronomy magazine has one where you can search for clubs in your area and join up with one of them, because they'll love to have you.

FLATOW: And you do "Star Gazers," do you not?

REGAS: Yes, yes, this is a program - folks might know the old "Star Gazer" program led by Jack Horkheimer...

FLATOW: Keep looking up.

REGAS: Exactly, keep looking up, and I can't believe I still pinch myself every time that I get to say those words afterwards. But this is the fellow that would appear on your PBS station, usually late at night, at weird hours, for a minute or five minutes telling you what's up in the sky. He'd sit on the rings of Saturn and point out at Jupiter, and he'd have this very interesting voice. It was great.

And so he passed away a few years ago, and the station has decided to continue the program. We've done a little bit of touching-up to it, but it's called "Star Gazers," and so you might catch us on weird hours on your PBS station, and they're always online at our website, stargazersonline.org, and you can watch any of the shows there, and we'll tell you what's up in the sky and say keep looking up. That's what we always say.

FLATOW: That's it. It's a great show. I've been watching it for years. I used to know Jack for a while, so...

REGAS: Oh, I know, what a great guy. I mean, this is a populizer of astronomy, and I just hope that I can fill his shoes a little bit and get people excited about the stars.

FLATOW: Well, good luck to you, Dean.

REGAS: Oh, thanks for having me. We've got to do this again in two weeks, before the Transit.

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